The present invention relates to inserts used in rotary cone drill bits and related drilling tools.
Background: Rotary Drilling
Oil wells and gas wells are drilled by a process of rotary drilling. In a conventional drill rig, as seen in FIG. 12 a drill bit 130 is mounted on the end of a drill string 132, made of many sections of drill pipe, which may be several miles long. At the surface a rotary drive turns the string, including the bit 136 at the bottom of the hole, while drilling fluid (or “mud”) is pumped through the string by very powerful pumps 134. The bit 136 is generally one of two types: either a rotary cone drill bit, such as the one seen in FIG. 10, or a fixed head bit, such as is seen in FIG. 11. These bits, which are generally formed of steel, will have structures for cutting or grinding the formation being drilled. One type of cutting or shearing structure is teeth, which are cut out of the steel of the bit body and generally coated with a hardfacing for wear resistance. For cutting or grinding, inserts formed of a harder material such as tungsten carbide are fastened into sockets specially formed within the bit to hold them.
When the bit wears out or breaks during drilling, it must be brought up out of the hole. This requires a process called “tripping”: a heavy hoist pulls the entire drill string out of the hole, in stages of (for example) about ninety feet at a time. After each stage of lifting, one “stand” of pipe is unscrewed and laid aside for reassembly (while the weight of the drill string is temporarily supported by another mechanism). Since the total weight of the drill string may be hundreds of tons, and the length of the drill string may be tens of thousands of feet, this is not a trivial job. One trip can require tens of hours and is a significant expense in the drilling budget. To resume drilling the entire process must be reversed. Thus the bit's durability is very important, to minimize round trips for bit replacement during drilling.
Background: Diamonds in Inserts
Diamonds have been used to enhance the hardness of inserts for a number of years. In one process, tiny polycrystalline diamonds (about 0.001 mm) are mixed with a metal and formed into a cylindrical buttons or compacts, which are used alone or bonded to a tungsten carbide post to form the insert.
In several patents, a flat layer of polycrystalline diamond material is bonded to a backing layer of a less hard material, such as tungsten carbide. Various embodiments of this are shown in Barr et al. (U.S. Pat. No. 5,025,874), Griffin (U.S. Pat. No. 5,111,895), Smith (U.S. Pat. No. 5,351,772)
Some processes enclose a core of ultra-hard material in a jacket of, for example, tungsten carbide (see Scott et al. (U.S. Pat. No. 5,348,108 and U.S. Pat. No. 5,248,006), Grimes et al. (U.S. Pat. No. 5,287,936), and Jurewicz, U.S. Pat. No. 5,273,125)). Other processes place the ultra-hard material as the outer layer, totally or partially covering a core of tungsten carbide, e.g. Waldenström et al. (U.S. Pat. No. 5,335,738 and U.S. Pat. No. 5,154,245), Tibbitts (U.S. Pat. No. 5,337,844), Tibbitts et al. (U.S. Pat. No. 5,279,375), and Keshavan et al.
Background: Tungsten Carbide
Tungsten carbide is produced in a number of different grades, with different sizes of tungsten particles, different binders, and different percentages of binder present. Generally, the formulations containing a larger percentage of binder are considered tougher (more fracture resistant) and easier to bond to, while a lower percentage of binder gives a harder and more wear resistant insert. Historically, when an overlying layer was to be added, the substrate would have a binder content of at least 13% to provide a good bond to the added layer.
Background: Inserts of Two Carbide Formulations Dispersed in each other
U.S. Pat. No. 4,956,012, which is owned by Newcomer Products, Inc., (one of the joint assignees) discloses a method of making drilling inserts by mixing nodules of pre-blended, un-sintered metal carbide/binder composites having certain desirable characteristics such as a very high hardness, oxidation resistance or gall resistance, and dispersing these nodules into other pre-blended, un-sintered and pelletized metal carbide/binder compositions having other desirable characteristics such as high toughness, corrosion resistance, or other property. The dispersion of the first composite into the second composite occurs prior to pressing and sintering of the mixture. In this manner, the integrity of the separate grades is maintained, while the properties of the new composite are enhanced.
Background: Layered Insert without Adhesive
U.S. Pat. No. 5,594,931, which is owned by Newcomer Products, Inc. (NPI), discloses an insert having a core made of a first grade of cobalt- or nickel-bonded tungsten carbide (typically a relatively tough composition) with a surface layer of a second grade of distinctively different cobalt- or nickel-bonded tungsten carbide (typically a hard, wear-resistant formulation). The bond between these layers is excellent without the need for an adhesive or transition layer.
Harder Inserts Having Seamless Diamond-Enhanced Surface
The present application discloses a shaped insert for a drilling tool, such as a drill bit, the insert having a diamond-enhanced layer which is seamlessly bonded over the working surface. Because of the technique used, the diamond-enhanced layer can be bonded to a substrate which contains less than the traditional 13% binder. This means that it is possible to have a harder insert initially and still be able to bond to it a layer which is enhanced with diamonds or other ultra-hard materials. In one embodiment, the substrate is composed of nodules of a harder grade of carbide dispersed within a less hard, more durable matrix of tungsten carbide, over which the layer having a superhard coating is applied. The coating, one embodiment of which contains bare diamonds and carbide, is coated onto a sintered or pre-sintered insert, which is then treated with a high temperature, high pressure process. No transition layer or adherent material is necessary to bond the ultra-hard layer onto the insert.
The disclosed innovations, in various embodiments, provide one or more of at least the following advantages:                the process is simple;        the bond is strong;        the performance is increased;        diamond-enhanced layer gives increased lifetime;        increased flexibility of deciding toughness/hardness of substrate.        